Rheostat



y- 1936- D. 1'. SIEGEL 2,040,278

RHEOSTAT Filed April 29, 1935 Y Patented .May 12, 1936 UNITED: srArE's PATENTOFFICE A BHEOSTAT David T. Siegel, Chicago, m. Application April 29, 1935, sci-n1 No. 18,785 15 Claims. (of. 201-55 My invention relates to rheostats and potentiometers and particularly to novel features of construction in the-contact arm, brush and the form of connection thereof with the operating shaft. a

This application is a continuation in part of myapplication Serial No. 702,343 filed Decemcember 14., 1933.

As stated'in the preamble, the object of my invention is to improve the construction of the movable elements of a rheostat, the particular improvements being pointed out in connection with the following detailed explanation.

The invention will be more readily understood by reference to the accompanying drawing in which Fig. 1 is a plan view of a rheostat constructed in accordance with my invention;

Fig. 2 is a longitudinal section view through the construction shown in Fig. i;

Fig. 3 is an assembly of the metal parts of the rheostat; v

' Fig. 4 is a perspective view of the porcelain sleeve constituting a part of the assembly;

-Fig. 5 is an enlarged sectional view showing the core, brush and an end of the contact arm; and

Fig. 6 is a sectional View of the line 6 6 of Fig. 2.

The device of my invention includes a base it of porcelain or similar dielectric material the base having aseat on which is seated the core li, wound with resistance wire l2. The base, core and wire, with the exception of the contact face of the wire are coated with an enamel slip, indicated at i3, and baked to fuse the enamel.

The'base is provided with an axial opening adapted to receive the operating shaft M. An

operating knob I5 is connected to one end of the shaft for rotating the same, the shaft-being rotatably mounted within a metal sleeve IS, the outer end of which is threaded to receive the clamping nut H. The sleeve is held against longitudinal movement on the shaft on one end by means of a split ring l8 that engages in a. circumferential groove in the shaft and on the opposite end by means of a disc I9 having a projection 20, the disc being held in place by i being pressed over the knurled or milled portion 2| of the shaft. The sleeve is held against rotation in the base by the following means: The axial recess in the base is somewhat enlarged at the point 22 and notches are provided in diametric opposite sides of the recess to engage with the projections 23 on a perforated washer 24.

This washer has a stop member 25 adapted to be engaged by the projection 20 to limit the turning movement of the shaft, the angular extent of the member 25 being selected to provide a predetermined sweep of the contact arm. The washer 24 also has a short projection 26 at the periphery of the opening therein, this last named projection engaging with a notch in the end flange 2i of the sleeve it. In Fig. 3 I have shown the washer in dotted lines in such position that the projection it is about to enter the notch in the flange 27. Thus the sleeve is held against rotation while the shaft is per.- mitted to freely rotate therein. 1

Mounted on the innerend of the shaft I4 is a porcelain sleeve Eli having a head 29 and di ametrically opposite projections 30 from the head. The shank or body 39 of the sleeve is cylindrical in form and fits over the shaft M. Notches 32 are provided in the head; the notches having communication with the axial opening in the sleeve. The outer end of the shaft I4 is upset or formed to extrude metal to form projections 33 that enter the notches 32 in the sleeve, this connection serving to prevent relative rotation between the shaft and sleeve.

The sweep arm or contact arm, as best shown in Figs. 1, 2, and 3, consists of a section of spring metal doubled on itself, the doubled portions having registering apertures of different size and shape. The straight or sweep portion 34 of the arm has an opening therein as shown in Fig. 1 that conforms to the contour of the head or driving hub 29 of the dielectric sleeve, the projections 30 on the sleeve serving as the means for effecting rotation of the arm. The shape of the opening is such that the arm is permitted fshaped metal member 31 is placed transversely of the arm and riveted in place, the head 38 of the rivet projecting into the cup-like space formed as the result of the construction described. The head 38 constitutes the bearing for a brush 39 of novel composition. This brush is composed of graphite as a substantial ingredient and finely divided metal impregnated therein. Inasmuch as the brush is indirect contact with the exposed surface of the resistance winding, its action in service is particularly satisfactory. The wire surface becomes polished and there ls no tendency towards deterioration or wear. Whatever unevenness may occur in the contact surface is compensated by the capacity of the brush to rock on the round head 38 of the rivet. This capacity is permitted by reason of the use of a flexible cable 40 preferably composed of braided or twisted fine wire, the cable being imbedded in the brush, as shown in Fig. 5, and at its opposite end soldered as at ll to a contact washer 42 that surrounds the cylindrical shank 3| of the dielectric sleeve. This washer has a projection 43 therein that engages a notch in the end of the rebent portion of the contact arm. This insures rotation of the washer with the arm. A coil spring 42a separates the washer and the flat rebentportion of the arm and provides for constant spring pressure tendency to hold the washer in electrical contact with the terminal member 44 that is seated on the base and held against rotation by means of the projection 45 thereon.

It will be noted that during assembly, or, if

desired, at any time thereafter, the nut I1 is actuated and this serves to pull inwardly the shaft and the dielectric sleeve and to compress the spring 42a. This serves to resiliently hold the contact washer against the terminal member with a firm pressure. This is the only sliding contact between the brush and the terminal, all the other connections being permanent.

. The contact arm and brush are electrically insulated from the shaft due to the interposition of the dielectric sleeve between the shaft and the contact members. The parts are so designed that stampings are used substantially entirely, and the devices will operate without the necessity for repairs for long periods of time. The relatively long resilient sweep arm, the graphite-metal brush mounted for rocking movement, the flexible direct connection between the brush and the terminal and the'complete insulation of the described parts from the operating shaft, all contribute towards the production of a rheostat that will be free of trouble throughout long periods of use.

An important advantage in the construction shown is that of wide separation of the line and grounded parts of the instrument; in that regard I refer to separation in terms of distance superficially. For example the end of the shaft i4 is countersunk in the head of the insulating sleeve and the distance between the shaft and the contact arm, measured on the outside surface of the insulating sleeve is relatively great. This is likewise true at the opposite end of the sleeve.

Many of the features described herein are applicable to other forms of electrical instruments such as switches, etc. and I do not wish to be limited, except as indicated in the appended claims.

I claim:

1. In combination, a base, resistance wires supported on said base, a shaft in the base, a contact arm connected to the shaft, means providing a cup on the end of said arm, a projection being provided on the floor of said cup, a brush seated within said cup and bearing on said projection with capacity for rocking movement thereon, a terminal, and a connection between the terminal and brush, the connection being sufficiently flexible to permit said brush to rock.

2. In combination, a base, resistance wires supported on said base, a shaft in the base. a contact arm connected to the shaft and insulatedtherefrom, means providing a cup on the end of said arm, a projection being provided on the floor of said cup, a brush seated within said cup and bearing on said projection with capacity for rocking movement thereon, a terminal and a connection between the terminal and brush, the connection being sufflciently flexible to permit said brush to rock.

3. In combination, a winding of resistance wire and means for supporting the same, a contact arm and means for rotating the same, a terminal, a contact member mounted to rotate on said terminal, a brush carried by said contact arm and separate therefrom, means for electrically connecting said brush to said contact member, said brush directly riding on said resistance winding and being composed of graphite as a substantial ingredient and metal impregnated therein.

4. In combination, a winding of resistance wire and means for supporting the same, a contact arm and means for rotating the same, a terminal, a contact member mounted to rotate on said terminal, a brush carried by said contact arm, a flexible conductor connecting said brush and said contact member, said brush riding directly on I a contact member mounted to rotate on said terminal, a brush carried by saidcontact arm, a flexible conductor permanently connected to said brush and said contact member, said brush riding directly on the resistance winding and being composed of graphite as a substantial ingredient and finely divided metal impregnated therein.

6. In a rheostat, the combination of a base and resistance wires associated therewith, a shaft journaled in the base, a contact arm, a terminal carried by the base and spaced from electrical contact with said shaft and electrically connected to said arm, a sleeve composed of dielectric material telescoped over said shaft and having a projection and recess connection to prevent relative rotation, said sleeve overlying a portion of the contact arm to hold the same in position and having a projection and recess connection with the arm to eifect the turning thereof.

7. In combination, a base and a resistance element associated therewith, a shaft journaled in the base, a contact arm, a terminal electrically connected to said arm, a sleeve composed of dielectric material carried by an end of said'shaft and connected thereto for rotation therewith, said connecting means constituting a stop member for limiting rotation of said shaft and arm, said sleeve serving to space said terminal from the shaft, said sleeve projecting through an opening in said arm and serving as the means for transmitting the rotation of the shaft to the arm.

8. In combination, a base and a resistance element supported thereby, a shaft Journaled in the base, a. contact arm composed of spring material and doubled on itself to form a loop, the looped portion having registering openings of different diameters, a sleeve composed of dielectric material non-rotatively connected to the shaft and having a shank and an enlarged end, the shank of said sleeve extending through both openings in said arm and the enlarged end of the sleeve projecting through the opening of largest diameter in said arm and having non-rotative en gagement therewith and overlying the material 75 serving to hold said am against axial displace ment from the shaft.

9. In combination, a base and a resistance element supported thereby, a shaft journaled in the base, a contact arm composed of spring material and doubled on itself to form a loop, the looped portion having registering openings of different diameters, a sleeve composed of dielectric material having an axial opening to receive the end of the shaft and a lateral recess to receive a projection from said shaft, said sleeve having a head being adapted to enter the larger of the registering openings in said arm and the projection on the head overlying the portion of said arm containing the opening of smaller diameter and serving to retain the armagainst agxial displacement on the shaft.

10. In a rheostat, the combination of a base and resistance wires associated therewith, a shaft jo'urnaled in the base, a contact arm, a terminal carried by the base and spaced-from electrical contact with said shaft and electrically connected .to said arm, a sleeve composed of dielectric ma- 11. In a rheostat, the combination with a baseand a winding of resistance wire supported thereon, a shaft carried by the base, asleeve composed of dielectric material non-rotatively connected to an end of said shaft, said sleeve having a head, a contact arm composed of spring material, means on the outer end of said arm providing. a contact surface for engagement with the resistance wire, the inner end of said arm being re-' bent, the arm and rebent portion of the arm having registering openings adapted to receive said sleeve, the opening in said rebent portion being of less diameter than the head on said sleeve, whereby said head overlies said rebent portion and retains said arm in place, andmeans plreventing relative rotation between the arm and eeve.

12. In a rheostat, the combination with abase and a winding of resistance wire supported thereon, a shaft carried by the base, a sleeve composed of. dielectric material mounted on an end of' said shaft and held against rotation relative thereto,

saiiifileevev having a non-round head, a contact arm composed of spring material, means .on the free end of said arm providing a contact .for engagement with the resistance wire, the opposite end of said am being doubled on itself to provide a u -sha'ped portion, said 'U-shaped por-' tion being punched to provide registering openings, the openingin the upper part of the U- shaped. portion being non-round to cooperate with-said head, the ope said .head whereby said head overlies said last named portion of the arm and is prevented'from separation from the shaft thereby.

' 13. In a rheostat, the combination with a base andawindingofresistanecwiresupportedthere-' inthelower partof, said U-shaped portion being of less diameter than on, a shaft carried by the base, a sleeve composed of dielectric material non-rotatively connected to an end of said shaft, said sleeve having a head, a contact arm composed of spring material, means on the outer end of said arm providing a contact surface for engagement with the resistance wire, the inner end of said arm being rebent, the arm and rebent portion of. the arm having registering openings adapted to receive. said sleeve, the opening in said rebent portion being of less diameter than the I head on said sleeve, whereby said head overlies said rebent portion and retains said arm in place, means preventing relative rotation between the arm and sleeve, said rebent portion being transversely bent to provide for spring compression between said head and a support, and means acting on said shaft for inducing said compression.

14. In a rheostat, the combination with a base and a winding of resistance wire supported thereon, a shaft carried by the base, a sleeve composed of dielectric material non-rotatively connected to an end of said shaft, said sleeve having a head and a cylindrical portion, a terminal piece secured to the base and having a recess in its inner end axially arranged relative to the cylindrical portion of said sleeve, a contact washer also having a recess axially arranged relative to said sleeveand overlying and in electrical contact relation to said terminal piece, at brush engaging said resistance wire and connected to said contact washer, a contact arm composed of spring material and having its free end constructed to support said brush, 'the opposite end of said arm beinggrebent, the arm and rebent portion of the arm having registering openings adapted to re- .ceive said sleeve, and to hold said am against rotation on said sleeve, the opening in the rebent portion being of less diameter than the head on the sleeve whereby said head overlies and clamps said rebent portion against said contact washer. 15. In a rheostat, the combination with a base and 'a winding of resistance wire supported thereon, a shaft carried by the base, a sleevecomposed of dielectric material non-rotatively to an end of said shaft, said sleeve having a head and a cylindrical portion. a terminal p'iecesecuredio the base and having a recess inits inner end axiallyarrange'd relative to the cylindrical portion of said sleeve, a contact washer having a recess. axially arranged relative, to said sleeve and overlying and in electrical contact relation to said terminal piece, a brush engaging said resistance wire and connected to said contact washer, a contact arm composed. of'spring material and having its free end constructed to support said brush, the opposite end of said .arm being rebent, the arm and rebent portion of the arm having registering openings adapted to receive said sleeve and to hold'said arm against rotation on said sleeve, the opening in the rebent portion being of less diameter than the head on' the sleeve whereby said head overlies and clamps said rebe'nt portion against said contact washer, said rebent portion beingtransversely bent to provide for spring. compression between said head and said washer, and means acting on said shaft for inducing said compression.

' DAVID '1. BIEGEL. 

